In numerous office machines such as printers, telecopiers, copying machines, etc., the printed sheets ejected by the office machine are deposited in a stack on an output tray for later retrieval. If successive sheets belonging to various processes or print jobs are deposited on the stack, the sheet groups corresponding to the individual processes are non-differentiated from one another. In order to obtain a desired sheet group for a particular print job, the sheets of the stack must be manually manipulated, or leafed through, to permit the individual sheets to be observed until the desired sheets are located within the stack. Such process requires a substantial amount of time and effort for obtaining the desired sheet group. This is the case, for example, where several work stations are connected to, and share, a common central printer.
It is known to attach a sorter comprising a multiplicity of stacking compartments on the sheet ejection side of an office machine so that the sheets associated with the various processes can each be deposited under control in separate stacking compartments. Such a sorter is complicated, requires much space and the number of available stacking trays and their holding capacities are limited. Furthermore, if the contents of the several stacking trays are removed together and transferred to a work station for further processing, the separated stacks are commonly combined in a single stack and must be separated again at the work station.
It is further known to insert paper sheets differing in color from the sheets of the stack between the sheet groups belonging to the various processes. The automatic insertion of the colored sheets is facilitated by storing the colored sheets in one of the trays provided in the office machine for the sheets to be printed.
Although the colored sheets within the stack enable the sheet groups to be ascertained visually, the output of the office machine is substantially reduced as the colored sheets occupy one of the storage trays of the office machine, and the number of available trays is limited. In addition, the colored sheets have the same format and dimensions as the sheets to be stacked. As a result, the colored sheets and the printed sheets are substantially aligned and the separation of the stack by means of the colored sheets is laborious. Furthermore, reusing the divided sheets is difficult as the colored sheets are exposed to the heat effect of the office machine printer mechanism.
It is also known to stack the particular successive sheet groups belonging to different processes such that successive sheet groups are offset alternately relative to each other (offset deposition). Through the use of relative offset deposition, the discrete sheet groups of the stack can be readily separated. However, when a sheet group corresponding to a particular process is removed from the stack, the two adjacent sheet groups originally disposed above and below the selected sheet group come into contact with one another. Due to the alternating offset deposition, the two adjacent sheet groups are not offset with respect to each other when engaged with one another, and they cannot be readily distinguished from each other.
Therefore, it would be highly desirable to have a new and improved method and device for separating groups of stacked sheets which enables the groups of stacked sheets to be readily distinguished from one another even when a selected group of sheets has been removed. Such a method and device should not substantially reduce the holding capacity of the associated office machinery, and should not be adversely affected by the heat effect of the office machine.